After freaking out for a while I did try it again thinking, why not, and it worked. I’ll have to work up my nerves to try it again. I am using an ELM327.Keep trying to connect/ write with FoCCCus - even if you can't turn the ignition on (eg. if you've got push button "START".) I was able to connect and FoCCCus eventually wrote everything required (even though the entire dash was dead and I wasn't able to turn the ignition to "ON".)
It's not a good situation to be in. Are you using a modified ELM327 interface?